JP7265189B2 - Powder containing low molecular weight polytetrafluoroethylene - Google Patents

Description

The present disclosure relates to powders comprising low molecular weight polytetrafluoroethylene.

Low-molecular-weight polytetrafluoroethylene (also called "polytetrafluoroethylene wax" or "polytetrafluoroethylene micropowder") with a molecular weight of several thousand to several hundred thousand has excellent chemical stability and extremely low surface energy. In addition, since fibrillation is unlikely to occur, it is used as an additive to improve the lubricity and the texture of the coating film surface in the production of plastics, inks, cosmetics, paints, greases, etc. (see, for example, Patent Document 1). .

As methods for producing low-molecular-weight polytetrafluoroethylene, a polymerization method, a radiation decomposition method, a thermal decomposition method, and the like are known. Conventionally, in radiolysis, low-molecular-weight polytetrafluoroethylene is generally obtained by irradiating high-molecular-weight polytetrafluoroethylene with radiation in an air atmosphere.

In addition, methods for reducing perfluorocarboxylic acids and salts thereof that can be produced as a by-product of radiolysis are also being investigated (see, for example, Patent Document 2).

JP-A-10-147617 JP 2018-24868 A

An object of the present disclosure is to provide a method for producing low-molecular-weight polytetrafluoroethylene in which the content of perfluorocarboxylic acids having 4 to 16 carbon atoms and salts thereof is reduced.
Another object of the present disclosure is to provide a novel low-molecular-weight polytetrafluoroethylene powder having a low content of perfluorooctanoic acid and its salts.

The present disclosure includes a polytetrafluoroethylene containing a perfluorocarboxylic acid having 4 to 16 carbon atoms or a salt thereof, and having a heat of fusion reduction rate of 40% or less from the first temperature rise to the second temperature rise in differential scanning calorimetry. In addition, the content of the perfluorocarboxylic acid and its salt is reduced by irradiating 5 to 1000 kGy of radiation at a temperature of less than 100 ° C. in the substantial absence of oxygen, and the melt viscosity at 380 ° C. The present invention relates to a method for producing low-molecular-weight polytetrafluoroethylene, including the step (1) of obtaining low-molecular-weight polytetrafluoroethylene of 1.0×10 ² to 7.0×10 ⁵ Pa·s.

Both the polytetrafluoroethylene and the low-molecular-weight polytetrafluoroethylene are preferably powders.

The present disclosure is a powder containing low-molecular-weight polytetrafluoroethylene, the content of perfluorooctanoic acid and its salt is 1500 mass ppb or less, and the low-molecular-weight polytetrafluoroethylene is 1.0 × 10 ² In the first derivative spectrum obtained by measuring the electron spin resonance method with a melt viscosity at 380 ° C. of ~ 7.0 × 10 ⁵ Pa · s, the signal intensity P1 with a g value of 2.020 and g It also relates to powders in which the difference (P1-P2) between the intensity P2 of the signal with a value of 2.023 is -0.07 or more.

The powder preferably has a specific surface area of 0.5 to 20 m ² /g.

According to the present disclosure, it is possible to provide a method for producing low-molecular-weight polytetrafluoroethylene in which the content of perfluorocarboxylic acid having 4 to 16 carbon atoms and its salt is reduced.
Moreover, according to the present disclosure, it is also possible to provide a novel low-molecular-weight polytetrafluoroethylene powder with a low content of perfluorooctanoic acid and its salts.

FIG. 4 is a diagram showing an example of P1 and P2 in an electron spin resonance (ESR) spectrum;

The present disclosure will be specifically described below.

The present disclosure includes a polytetrafluoroethylene containing a perfluorocarboxylic acid having 4 to 16 carbon atoms or a salt thereof, and having a heat of fusion reduction rate of 40% or less from the first temperature rise to the second temperature rise in differential scanning calorimetry. At 380° C., the content of the perfluorocarboxylic acid and its salts was reduced by irradiating (PTFE) with radiation of 5 to 1000 kGy at a temperature of less than 100° C. in the substantial absence of oxygen. A method for producing low-molecular-weight polytetrafluoroethylene, comprising the step (1) of obtaining low-molecular-weight polytetrafluoroethylene (low-molecular-weight PTFE) having a melt viscosity of 1.0×10 ² to 7.0×10 ⁵ Pa·s. Regarding.
According to the production method of the present disclosure, low-molecular-weight PTFE in which the content of the perfluorocarboxylic acid and its salt is reduced can be obtained from PTFE containing a perfluorocarboxylic acid having 4 to 16 carbon atoms or a salt thereof. .
It is believed that the irradiation with the specific dose of radiation decomposes the perfluorocarboxylic acid and its salt contained in the PTFE to be irradiated. In addition, since the irradiation is carried out substantially in the absence of oxygen, even if the PTFE is partially decomposed by the irradiation, it is considered that the perfluorocarboxylic acid or its salt is unlikely to be newly formed. As a result, it is believed that low-molecular-weight PTFE in which the content of the perfluorocarboxylic acid and its salt is reduced can be obtained.
In addition, since the manufacturing method of the present disclosure does not require heating at a high temperature, there is no need to introduce heating equipment. Moreover, a process such as moving the obtained low-molecular-weight PTFE from the irradiation equipment to the heating equipment is not necessary. Therefore, productivity can be improved and manufacturing costs can be suppressed.

The PTFE to be irradiated with radiation in step (1) has a heat of fusion reduction rate of 40% or less from the first temperature rise to the second temperature rise in differential scanning calorimetry. The heat of fusion reduction rate is an index of the molecular weight of PTFE, and the larger the heat of fusion reduction rate, the higher the molecular weight tends to be.
The heat of fusion reduction rate is preferably 35% or less, more preferably 30% or less, and even more preferably 27% or less, and may be -30% or more, -20 % or more.
The heat of fusion reduction rate is a value obtained by measurement using a differential scanning calorimeter (DSC, trade name: DSC7020, manufactured by Hitachi High-Tech Science Co., Ltd.). Specifically, about 10 mg of PTFE was precisely weighed, placed in a special aluminum pan, heated to 200°C in a nitrogen atmosphere, held for 5 minutes, and further heated to 390°C at a rate of 10°C/min. The temperature is raised (first temperature rise) to sufficiently melt the crystals, and the heat of fusion is measured. Next, after the temperature is lowered from 390°C to 200°C at a rate of 10°C/min, the temperature is raised from 200°C to 390°C at a rate of 10°C/min (second temperature rise) to measure the heat of fusion. Using the measured values of the heat of fusion at the time of the first temperature rise and at the time of the second temperature rise, the reduction rate of the heat of fusion is calculated by the following formula.
Reduction rate of heat of fusion (%) = (heat of fusion at first temperature rise - heat of fusion at second temperature rise) / (heat of fusion at first temperature rise) x 100

PTFE having the above reduction rate of heat of fusion can be produced, for example, by radiolyzing or thermally decomposing high-molecular-weight PTFE. The radiation decomposition or thermal decomposition may be performed in any atmosphere, for example, in air, in an inert gas, in vacuum, or the like. From the viewpoint of low cost, implementation in the air is preferable, and from the viewpoint of difficulty in generating perfluorocarboxylic acids having 4 to 16 carbon atoms and salts thereof, implementation in the absence of substantially oxygen is preferable. . However, since the production method of the present disclosure includes the step (1), it is not essential to carry out the radiation decomposition or thermal decomposition substantially in the absence of oxygen. It may also be carried out in the presence of oxygen (eg in air).
The high molecular weight PTFE preferably has a standard specific gravity (SSG) of 2.130 to 2.230. The standard specific gravity (SSG) is a value measured according to ASTM D4895.
The PTFE can also be produced directly by polymerizing tetrafluoroethylene (TFE). In this case, the rate of decrease in the heat of fusion can be set within the above range by selecting the initiator and adjusting the polymerization temperature and polymerization time.

The PTFE contains a perfluorocarboxylic acid having 4 to 16 carbon atoms or a salt thereof.
The perfluorocarboxylic acid or its salt may be used for PTFE polymerization. Moreover, when the above-mentioned high-molecular-weight PTFE is subjected to radiolysis in an air atmosphere, the perfluorocarboxylic acid or its salt is usually produced. According to the production method of the present disclosure, even when such PTFE containing the perfluorocarboxylic acid or its salt is used as a raw material for some reason, the content of the perfluorocarboxylic acid and its salt can be obtained low-molecular-weight PTFE reduced.
In the PTFE, the content (total amount) of the perfluorocarboxylic acid and its salt may be 5 mass ppb or more, may be greater than 10 mass ppb, or may be greater than 15 mass ppb, may be greater than 20 mass ppb, may be greater than or equal to 25 mass ppb, may be greater than 50 mass ppb, may be greater than 100 mass ppb, may be greater than 500 mass ppb, It may be greater than 1000 mass ppb, may be greater than 2000 mass ppb, may be greater than 3000 mass ppb, or may be greater than 10000 mass ppb.
The amount of perfluorocarboxylic acid and its salt can be measured by liquid chromatography.

The PTFE may contain perfluorooctanoic acid or a salt thereof. The content of perfluorooctanoic acid and its salt in the PTFE may be, for example, 5 mass ppb or more, may be greater than 10 mass ppb, may be greater than 15 mass ppb, or may be greater than 20 mass ppb. may be 25 mass ppb or more, may be greater than 50 mass ppb, may be greater than 100 mass ppb, may be greater than 300 mass ppb, may be greater than 500 mass ppb or greater than 1500 mass ppb.
The amount of perfluorooctanoic acid and its salt can be measured by liquid chromatography.

The PTFE may contain perfluorosulfonic acid having 4 to 16 carbon atoms or a salt thereof. In the PTFE, the total amount of the perfluorosulfonic acid and its salt may be 5 mass ppb or more, may be more than 10 mass ppb, may be more than 15 mass ppb, or may be more than 20 mass ppb. may be 25 mass ppb or more.
The amount of perfluorosulfonic acid and its salt can be measured by liquid chromatography.

Although the shape of the PTFE is not particularly limited, it is preferably powder.

The dose of radiation in step (1) is 5-1000 kGy. The dose is preferably 10 kGy or more, more preferably 20 kGy or more, still more preferably 30 kGy or more, and particularly preferably 50 kGy or more, in that low-molecular-weight PTFE with a smaller amount of the perfluorocarboxylic acid and its salt can be obtained. Moreover, the dose is preferably 500 kGy or less, more preferably 300 kGy or less, still more preferably less than 250 kGy, and particularly preferably 200 kGy or less, in order to obtain low-molecular-weight PTFE having a moderately high molecular weight.
The above dose means absorbed dose.

The radiation is not particularly limited as long as it is ionizing radiation, and includes electron beams, gamma rays, X-rays, neutron beams, high-energy ions and the like, but electron beams and gamma rays are preferred.

The irradiation temperature of the radiation is less than 100°C. The irradiation temperature is preferably less than 70°C, more preferably less than 50°C, and preferably 5°C or higher.
It is economically preferable to irradiate at room temperature. Normal temperature may be in the temperature range of 5 to 60°C, including radiation heat generation, preferably 10 to 50°C, more preferably 10 to less than 50°C, and 15 to 45°C. is more preferred.
According to the production method of the present disclosure, treatment at such a relatively low temperature can sufficiently reduce the perfluorocarboxylic acid and its salt.

The irradiation in step (1) is carried out substantially in the absence of oxygen. Here, "substantially free of oxygen" means that the oxygen concentration in the atmosphere in which the process is carried out is 0.5% by volume or less. The oxygen concentration is preferably 0.25% by volume or less, more preferably 0.1% by volume or less, in that low-molecular-weight PTFE with a smaller amount of the perfluorocarboxylic acid and its salt can be obtained. It is preferably 0.01% by volume or less, and particularly preferably 0.001% by volume or less. The lower limit is not particularly limited, and may be a concentration below the detection limit.
The oxygen concentration is measured by a method of analyzing the gas phase portion in the space where the process is performed by gas chromatography, a method using an oxygen concentration meter, or a method of examining the color tone of the oxygen detector installed in the space. can.

The irradiation in step (1) is preferably carried out in a closed container. The closed container is a container that can be closed so that the oxygen concentration in the container can be adjusted. Therefore, it may be connected to a pipe for sucking and discharging an inert gas or for discharging the gas in the closed container, and a pipe, lid, valve, flange, etc. that is not opened during irradiation may be connected. may Moreover, the shape is not particularly limited, and may be cylindrical, prismatic, spherical, or the like, and may be a bag with a variable internal volume. Also, the material thereof is not particularly limited, and may be metal, glass, polymer, or the like. The sealed container should be of a material and structure that is permeable to radiation and not degraded by irradiation of radiation, but does not need to be a pressure-resistant container.

The manufacturing method of the present disclosure may include, prior to step (1), the step of charging the PTFE into a closed container in the substantial absence of oxygen. Putting into the closed container in the absence of substantially oxygen means that the oxygen concentration in the atmosphere inside the closed container after putting is within the range described above.

As a method of putting the PTFE into a closed container substantially in the absence of oxygen, for example, the PTFE and at least one selected from the group consisting of an inert gas and an oxygen adsorbent are put into the closed container. method.

Examples of the method of introducing each of the above substances into the closed container include a method of placing the PTFE in the closed container and then filling the closed container with the inert gas or evacuating the closed container. . When the oxygen adsorbent is used, a method of installing the PTFE and the oxygen adsorbent in the airtight container and then sealing the closed container, or a method of placing the PTFE and the oxygen adsorbent in the closed container After installing the oxygen adsorbent, the inside of the closed container is filled with the inert gas, after installing the PTFE and the oxygen adsorbent in the closed container, the inside of the closed container is evacuated, and the like. be done.

The inert gas must be inert to the decomposition reaction of the perfluorocarboxylic acid and its salt (and the PTFE) due to radiation exposure. Examples of the inert gas include gases such as nitrogen, helium, and argon. Among them, nitrogen is preferable.

The inert gas preferably has an oxygen content of 0.5% by volume or less, more preferably 0.25% by volume or less, even more preferably 0.1% by volume or less. It is even more preferably 0.01% by volume or less, and particularly preferably 0.001% by volume or less. The lower limit is not particularly limited, and may be an amount below the detection limit. When the content of oxygen in the inert gas is within the above range, low-molecular-weight PTFE with a smaller amount of perfluorocarboxylic acid and its salt can be obtained.
The above-mentioned oxygen content can be confirmed by an oxygen concentration meter or oxygen detection paper as well as analysis by gas chromatography.

The oxygen adsorbent is not particularly limited as long as it has a function of adsorbing oxygen. Known oxygen adsorbents such as organic oxygen adsorbents such as activated carbon-based oxygen adsorbents can be used. The oxygen adsorbent may be of the moisture-dependent type that requires moisture when reacting with oxygen or the self-reacting type that does not require moisture, but the self-reacting type is preferable. As the oxygen adsorbent, an iron-based self-reacting oxygen adsorbent, quicklime, or the like is preferable, and an iron-based self-reacting oxygen adsorbent is particularly preferable.

It is preferable that the amount of the oxygen adsorbent charged is an amount that allows the oxygen concentration in the closed container to fall within the range described above.

The irradiation in step (1) is preferably carried out substantially in the absence of halogenated polymers having halogen atoms other than fluorine atoms.
The above halogenated polymers include polymers having fluorine atoms as well as halogen atoms other than fluorine atoms.
Examples of the halogenated polymer include polymers having chlorine atoms, such as polyvinyl chloride (PVC), polyvinylidene chloride (PVdC), and polychlorotrifluoroethylene (PCTFE).
“Substantially free of the halogenated polymer” means that the amount of the halogenated polymer present is less than 0.001% by mass relative to the PTFE. The abundance is preferably 0.0001% by mass or less. Although the lower limit is not particularly limited, it may be an amount below the detection limit.

It is also preferred that the irradiation in step (1) is carried out substantially in the absence of hydrocarbons, chlorinated hydrocarbons, alcohols and carboxylic acids.
Examples of the above hydrocarbons include saturated hydrocarbons having 1 to 20 carbon atoms.
Examples of the chlorinated hydrocarbons include chlorinated saturated hydrocarbons having 1 to 18 carbon atoms.
Examples of the alcohol include monohydric saturated alcohols having 1 to 12 carbon atoms.
Examples of the carboxylic acid include saturated monocarboxylic acids having 1 to 13 carbon atoms.
The fact that the compound is substantially absent means that the abundance (total amount) of the compound is less than 0.001% by mass relative to the PTFE. The abundance is preferably 0.0001% by mass or less. Although the lower limit is not particularly limited, it may be an amount below the detection limit.

In step (1), low-molecular-weight PTFE in which the content of perfluorocarboxylic acid having 4 to 16 carbon atoms and its salt is reduced is obtained. In other words, the content of the perfluorocarboxylic acid and its salt in the low-molecular-weight PTFE is less than the content in the PTFE before irradiation in step (1).

In step (1), the reduction rate (PFC reduction rate) of perfluorocarboxylic acid having 4 to 16 carbon atoms and its salt (PFC) is preferably 10% by mass or more, more preferably 20% by mass or more. It is preferably 30% by mass or more, still more preferably 40% by mass or more, and particularly preferably 50% by mass or more. The higher the PFC reduction rate, the better, and the upper limit is not particularly limited, but may be 100% by mass.
The PFC reduction rate is obtained by measuring the PFC content in the PTFE before irradiation in step (1) and the low-molecular-weight PTFE obtained in step (1) by liquid chromatography, and using these measured values, the following formula demand.
PFC reduction rate (% by mass) = (PFC content in PTFE before irradiation - PFC content in obtained low-molecular-weight PTFE)/(PFC content in PTFE before irradiation) x 100

In step (1), it is also possible to obtain low-molecular-weight PTFE with a reduced content of perfluorooctanoic acid and its salts. In other words, the content of perfluorooctanoic acid and its salt in the low-molecular-weight PTFE can be made smaller than the content in the PTFE before irradiation in step (1).

In step (1), the reduction rate of perfluorooctanoic acid and its salt (PFOA) (PFOA reduction rate) is preferably 10% by mass or more, more preferably 20% by mass or more, and 30% by mass or more. is more preferably 40% by mass or more, and particularly preferably 50% by mass or more. The higher the PFOA reduction rate, the better, and the upper limit is not particularly limited, but may be 100% by mass.
The PFOA reduction rate is obtained by measuring the PFOA content in the PTFE before irradiation in step (1) and the low-molecular-weight PTFE obtained in step (1) by liquid chromatography, and using these measured values according to the following formula: demand.
PFOA reduction rate (% by mass) = (content of PFOA in PTFE before irradiation - content of PFOA in obtained low-molecular-weight PTFE)/(content of PFOA in PTFE before irradiation) x 100

In the low-molecular-weight PTFE obtained in step (1), the content (total amount) of perfluorocarboxylic acids having 4 to 16 carbon atoms and salts thereof may be 10000 mass ppb or less, and 3000 mass ppb or less. may be 2000 mass ppb or less, may be 1000 mass ppb or less, may be 500 mass ppb or less, may be 100 mass ppb or less, or may be 50 mass ppb or less; may be less than 25 mass ppb, may be 20 mass ppb or less, may be 15 mass ppb or less, may be 10 mass ppb or less, may be less than 5 mass ppb good too. The lower limit is not particularly limited, and may be an amount below the detection limit.
The amount of perfluorocarboxylic acid and its salt can be measured by liquid chromatography.

In the low-molecular-weight PTFE, the content of perfluorooctanoic acid and salts thereof may be 1500 mass ppb or less, 500 mass ppb or less, 300 mass ppb or less, or 100 mass ppb or less. It may be ppb or less, may be 50 mass ppb or less, may be less than 25 mass ppb, may be 20 mass ppb or less, may be 15 mass ppb or less, or may be 10 mass ppb or less. It may be ppb or less, or may be less than 5 mass ppb. The lower limit is not particularly limited, and may be an amount below the detection limit.
The amount of perfluorooctanoic acid and its salt can be measured by liquid chromatography.

In the low-molecular-weight PTFE, the amount of perfluorosulfonic acid having 4 to 16 carbon atoms and a salt thereof may be less than 25 mass ppb, may be 20 mass ppb or less, or may be 15 mass ppb or less. may be 10 mass ppb or less, or less than 5 mass ppb. The lower limit is not particularly limited, and may be an amount below the detection limit.
The amount of perfluorosulfonic acid and its salt can be measured by liquid chromatography.
The low-molecular-weight PTFE may contain less perfluorosulfonic acid and its salt than the PTFE to be irradiated.

The low-molecular-weight PTFE has a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s. The melt viscosity is preferably 1.5×10 ³ Pa·s or more, more preferably 7.0×10 ³ Pa·s or more, and 3.0×10 ⁵ Pa·s or less. It is preferably 1.0×10 ⁵ Pa·s or less, more preferably 9.0×10 ⁴ Pa·s or less.

The above-mentioned melt viscosity is determined according to ASTM D 1238 using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die, and a 2g sample preheated at 380°C for 5 minutes under a load of 0.7MPa. It is a value measured while maintaining the above temperature.

The low-molecular-weight PTFE preferably has a melting point of 320 to 340°C, more preferably 324 to 336°C.

The above melting point was measured using a differential scanning calorimeter (DSC), and after temperature calibration in advance using indium and lead as standard samples, about 3 mg of low-molecular-weight PTFE was placed in an aluminum pan (crimped container), and 200 ml/ The temperature range from 250 to 380° C. is raised at a rate of 10° C./min under an air current of 10 min.

The low-molecular-weight PTFE may be homo-PTFE consisting only of tetrafluoroethylene (TFE) units, or modified PTFE containing modified monomer units based on modified monomers copolymerizable with TFE units and TFE. . In the manufacturing method of the present disclosure, the composition of the polymer does not change, so the low-molecular-weight PTFE has the same composition as the PTFE.

In the modified PTFE, the content of the modified monomer units is preferably 0.001 to 1% by mass, more preferably 0.01% by mass or more, and 0.5% by mass of the total monomer units. The following are more preferable, and 0.1% by mass or less is even more preferable. As used herein, the modified monomer unit means a portion of the molecular structure of the modified PTFE and is derived from the modified monomer, and the total monomer unit refers to all monomers in the molecular structure of the modified PTFE. means a part derived from the body. The content of modified monomer units can be determined by a known method such as Fourier transform infrared spectroscopy (FT-IR).

The modified monomer is not particularly limited as long as it can be copolymerized with TFE. Examples include perfluoroolefins such as hexafluoropropylene [HFP]; chlorofluoroolefins such as chlorotrifluoroethylene [CTFE]; Hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF]; perfluorovinyl ether; perfluoroalkylethylene; ethylene and the like. Moreover, one type of modifying monomer may be used, or a plurality of types thereof may be used.

The perfluorovinyl ether is not particularly limited, and for example, the following general formula (1)
CF ₂ = CF-ORf (1)
(wherein Rf represents a perfluoro organic group), and the like. As used herein, the above-mentioned "perfluoro organic group" means an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoro organic group may have an ether oxygen.

Examples of the perfluorovinyl ether include perfluoro(alkyl vinyl ether) [PAVE], in which Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms in the general formula (1). The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

Examples of the perfluoroalkyl group in PAVE include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, and perfluorohexyl group. Purpleolo(propyl vinyl ether) [PPVE], in which the group is a perfluoropropyl group, is preferred.

As the perfluorovinyl ether, further, in the general formula (1), Rf is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and Rf is the following formula:

(Wherein, m represents an integer of 0 or 1 to 4), and Rf is the following formula:

(wherein n represents an integer of 1 to 4).

Perfluoroalkylethylene is not particularly limited, and examples thereof include (perfluorobutyl)ethylene (PFBE), (perfluorohexyl)ethylene, (perfluorooctyl)ethylene and the like.

The modified monomer in the modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PPVE, PFBE and ethylene. More preferably, it is at least one selected from the group consisting of HFP and CTFE.

Although the shape of the low-molecular-weight PTFE is not particularly limited, it is preferably powder. It is also preferable that both the PTFE and the low-molecular-weight PTFE are powders.

The production method of the present disclosure may further include the step of exposing the low-molecular-weight PTFE obtained in step (1) to air.
The time from the end of the radiation irradiation in step (1) to the exposure of the low-molecular-weight PTFE to air may be, for example, less than 1 day, less than 10 hours, or less than 1 hour. , less than 10 minutes, or less than 5 minutes.

In the production method of the present disclosure, the PTFE and the low-molecular-weight PTFE are preferably not placed at a temperature of 100°C or higher, preferably not placed at a temperature of 70°C or higher, and not placed at a temperature of 50°C or higher. None is also preferred.
The PTFE and the low-molecular-weight PTFE are preferably kept at the above temperature for no longer than 30 minutes, preferably no longer than 10 minutes, and preferably no longer than 10 seconds.

The production method of the present disclosure can further include a step of pulverizing the low-molecular-weight PTFE obtained in step (1). The pulverization method is not particularly limited, and conventionally known methods can be employed.

The low-molecular-weight PTFE obtained by the production method of the present disclosure is further described below.

When the low-molecular-weight PTFE is powder, the average particle size is preferably 0.5 to 200 μm, more preferably 100 μm or less, even more preferably 50 μm or less, even more preferably 25 μm or less, and particularly preferably 10 μm or less. Since the powder has a relatively small average particle size, it is possible to form a coating film having superior surface smoothness, for example, when it is used as an additive for paint.

The average particle size is measured using a laser diffraction particle size distribution analyzer (HELOS & RODOS) manufactured by JEOL Ltd., without using a cascade, at a dispersion pressure of 3.0 bar, and corresponds to 50% of the integrated particle size distribution. equal to the particle size.

When the low-molecular-weight PTFE is powder, it preferably has a specific surface area of 0.5 to 20 m ² /g.
The low-molecular-weight PTFE powder includes a low specific surface area type having a specific surface area of 0.5 m ² /g or more and less than 7.0 m ² /g, and a specific surface area type having a specific surface area of 7.0 m ² /g or more and 20 m ² /g or less. A type with a high specific surface area is required.
A low-molecular-weight PTFE powder with a low specific surface area has the advantage of being easily dispersed in a matrix material such as paint, but has a large dispersed particle size in the matrix material and is poor in fine dispersion.
The specific surface area of the low-molecular-weight PTFE powder having a low specific surface area is preferably 1.0 m ² /g or more, preferably 5.0 m ² /g or less, and more preferably 3.0 m ² /g or less. As the matrix material, in addition to plastics and inks, paints and the like are preferably used.
Low-molecular-weight PTFE powder of a type with a high specific surface area, for example, when dispersed in a matrix material such as paint, has a small dispersed particle size in the matrix material, and has the effect of modifying the surface, such as improving the texture of the surface of the coating film. However, it may not easily disperse due to the long time required for dispersing it in the matrix material, and the viscosity of the paint or the like may increase.
The specific surface area of the low-molecular-weight PTFE powder having a high specific surface area is preferably 8.0 m ² /g or more, preferably 25 m ² /g or less, and more preferably 20 m ² /g or less. As the matrix material, in addition to oils, greases, and paints, plastics and the like are preferably used.

The above specific surface area is measured using a surface analyzer (trade name: BELSORP-miniII, manufactured by Microtrack Bell Co., Ltd.), using a mixed gas of 30% nitrogen and 70% helium as a carrier gas, and using liquid nitrogen for cooling. , measured by the BET method.

The low-molecular-weight PTFE may have a carboxyl group at the molecular chain end. The number of carboxyl groups is not particularly limited, but may be, for example, 0 to 500 per 10 ⁶ carbon atoms in the main chain.
The number of carboxyl groups can be measured by the following method. The detection limit by this measurement method is 0.5.
(Measuring method)
The following measurements are performed according to the terminal group analysis method described in JP-A-4-20507.
A low-molecular-weight PTFE powder is preformed in a hand press to produce a film approximately 0.1 mm thick. Infrared absorption spectrum analysis is performed on the produced film. Infrared absorption spectrum analysis is also performed on PTFE whose ends are completely fluorinated by contacting PTFE with fluorine gas, and the number of terminal carboxyl groups is calculated from the difference spectrum between the two by the following equation.
Number of terminal carboxy groups (per 10 ⁶ carbon atoms) = (l x K)/t
l: Absorbance K: Correction coefficient t: Film thickness (mm)
The absorption frequency of the carboxy group is 3560 cm ⁻¹ and the correction factor is 440.

An unstable terminal group derived from the chemical structure of the polymerization initiator or chain transfer agent used in the polymerization reaction of the PTFE or the high-molecular-weight PTFE may occur at the molecular chain end of the low-molecular-weight PTFE. The unstable terminal group is not particularly limited, and examples thereof include -CH ₂ OH, -COOH, -COOCH ₃ and the like.

The low-molecular-weight PTFE may have stabilized unstable terminal groups. The method for stabilizing the unstable terminal group is not particularly limited, and includes, for example, a method of exposing the terminal to a fluorine-containing gas to convert the terminal to a trifluoromethyl group [--CF ₃ ].

The low-molecular-weight PTFE may also be terminally amidated. The terminal amidation method is not particularly limited. A method of contacting with ammonia gas and the like can be mentioned.

When the above-mentioned low-molecular-weight PTFE has stabilized unstable terminal groups or amidated terminals, it is used as an additive to a mating material such as paints, greases, cosmetics, plating solutions, toners, plastics, etc. In addition, it is easy to match with the mating material and can improve dispersibility.

The manufacturing method of the present disclosure may further include a step (M1) of obtaining a molded article by heating high-molecular-weight polytetrafluoroethylene to its primary melting point or higher before step (1).
The primary melting point is preferably 300° C. or higher, more preferably 310° C. or higher, and even more preferably 320° C. or higher.
The primary melting point means the maximum peak temperature of the endothermic curve appearing on the crystal melting curve when the unsintered high-molecular-weight PTFE is measured with a differential scanning calorimeter. The endothermic curve was obtained by using a differential scanning calorimeter to raise the temperature at a temperature elevation rate of 10° C./min.

The molded article in step (M1) preferably has a specific gravity of 1.0 g/cm ³ or more, more preferably 1.5 g/cm ³ or more, and 2.5 g/cm ³ or less. is preferred. When the specific gravity of the molded article is within the above range, pores and unevenness on the surface are reduced, and as a result, low-molecular-weight PTFE with a small specific surface area can be obtained.
The above specific gravity can be measured by a water substitution method.

After the step (M1), the molded product obtained in the step (M1) is further subjected to radiolysis or thermal decomposition, so that the reduction rate of the heat of fusion from the first temperature rise to the second temperature rise in differential scanning calorimetry is It is preferable to carry out the step (M2) of obtaining PTFE that is 40% or less.
In this case, the PTFE obtained in step (M2) can be used as the PTFE in step (1).
The radiation decomposition or thermal decomposition may be performed in any atmosphere, for example, in air, in an inert gas, in vacuum, or the like. From the viewpoint of low cost, implementation in the air is preferable, and from the viewpoint of difficulty in generating perfluorocarboxylic acids having 4 to 16 carbon atoms and salts thereof, implementation in the absence of substantially oxygen is preferable. . However, since the production method of the present disclosure includes the step (1), it is not essential to carry out the radiation decomposition or thermal decomposition substantially in the absence of oxygen. It may also be carried out in the presence of oxygen (eg in air).
In addition, when the above-described step of charging the PTFE into a closed container substantially in the absence of oxygen is also performed, the steps (M1) and (M2) are preferably performed before the charging step. .

The manufacturing method of the present disclosure may further include a step of pulverizing the molded product to obtain powder after step (M1) and before step (M2). The molded product may be coarsely pulverized and then finely pulverized.

The present disclosure is a powder containing low-molecular-weight polytetrafluoroethylene, the content of perfluorooctanoic acid and its salt is 1500 mass ppb or less, and the low-molecular-weight polytetrafluoroethylene is 1.0 × 10 ² The intensity P1 of the signal with a g value of 2.020 in the first derivative spectrum obtained by electron spin resonance (ESR) measurement with a melt viscosity at 380 ° C. of ~7.0 × 10 ⁵ Pa s and the difference (P1-P2) between the intensity P2 of the signal with a g value of 2.023 is -0.07 or more.

The low-molecular-weight PTFE in the powder of the present disclosure exhibits the above specific signal in a first-order differential spectrum (hereinafter also referred to as ESR spectrum) obtained by measurement by electron spin resonance (ESR).
Low molecular weight PTFE obtained by conventional methods such as irradiation in the presence of oxygen does not show the above specific signal. It is presumed that the structure and ratio of radicals contained in the low-molecular-weight PTFE obtained by the conventional method are different from the low-molecular-weight PTFE in the powder of the present disclosure.

First, the ESR measurement conditions and definitions of related terms will be described.
Measurement conditions are as follows.
Apparatus: JES-FR30EX manufactured by JEOL Ltd.
Measurement temperature: 23±3°C
Microwave frequency: 9.42GHz
Microwave output: 0.4mW
Central magnetic field: 347.548mT
Sweep width: ±25mT
Sweep time: 60s
Time constant: 0.03s
Magnetic field modulation width: 0.32mT
Number of scans: 1 Modulation frequency: 100 kHz
Marker: Mn2 ⁺

In the ESR spectrum, the vertical axis is the corrected signal intensity, and the horizontal axis is the g value.
The above corrected signal strength is calculated by the following formula:
Corrected signal intensity (mg ⁻¹ )=Int. [PTFE]/Int. [Mn ²⁺ ]/sample mass (mg)
(wherein Int.[PTFE] is the signal intensity of the sample before correction, and Int.[Mn ²⁺ ] is the signal intensity of the marker).
In this specification, unless otherwise specified, when the signal of the ESR spectrum of PTFE is simply referred to as the intensity, it refers to the corrected signal intensity.
The g value of the ESR signal is given by the following formula:
g=hν/βH
(wherein h is the Planck constant, ν is the frequency of the electromagnetic wave to be measured, β is the Bohr magneton, and H is the magnetic field strength from which the signal is obtained).
The g value was corrected based on the known g values 2.034 and 1.981 corresponding to the third and fourth peaks from the low magnetic field side among the six peaks of Mn ²⁺ used as markers. use the value.
When the baseline of the ESR spectrum shifts, baseline correction is performed so that the signal intensity near g values of 2.05 and 1.98 becomes approximately zero.
In the ESR spectrum, a positive signal means a signal appearing in the positive region (above the baseline) of the spectrum, and a negative signal means a signal appearing in the negative region (below the baseline) of the spectrum. I mean the signal that appears.

The low-molecular-weight PTFE in the powder of the present disclosure has a difference (P1-P2) between the signal intensity P1 at a g value of 2.020 and the signal intensity P2 at a g value of 2.023 in the ESR spectrum is -0. .07 or greater.
The signal with a g-value of 2.020 and the signal with a g-value of 2.023 may be positive signals. Also, P1 and P2 may be the absolute values of the intensity of the signal.

（式中の波線はＰＴＦＥのポリマー鎖を示す。以下同様）で示されるラジカル１に基づく信号であり、ｇ値が２．０２３の信号（ピーク）は、下記式：

で示されるラジカル２に基づく信号であると考えられる。
上記融解熱の減少率が４０％以下である、低分子量化されたＰＴＦＥは、ラジカル１及びラジカル２を含む。
その後、実質的に酸素不存在下で照射を行うと（工程（１））、ラジカル２の一部は照射によって分解されてラジカル１に変化するため、ラジカル１の割合が多くなる傾向にある。
他方、上記照射を空気中で行うと、ラジカル１及びラジカル２が生成するため、ラジカル１の割合は多くならない。 The signal (peak) with a g-value of 2.020 is
The formula below:

(The wavy line in the formula indicates the polymer chain of PTFE. The same applies hereinafter) is a signal based on the radical 1 shown in the following formula:

It is considered that the signal is based on the radical 2 represented by .
The low-molecular-weight PTFE having a heat of fusion reduction rate of 40% or less contains Radical 1 and Radical 2.
After that, when irradiation is performed in substantially the absence of oxygen (step (1)), some of the radicals 2 are decomposed by the irradiation and changed to radicals 1, so the proportion of radicals 1 tends to increase.
On the other hand, if the irradiation is performed in the air, radicals 1 and 2 are generated, so the proportion of radical 1 does not increase.

As described in the examples below, the production method of the present disclosure allows the difference P1-P2, which was less than -0.07 before irradiation (Comparative Example 2), to be -0.07 or more after irradiation (Example 1, etc.). , means that radicals 2 are reduced and radicals 1 are increased by the irradiation in step (1).
The fact that the difference P1−P2 is −0.07 or more means that the difference in the abundance of radicals 1 and 2 in the low-molecular-weight PTFE is at least a certain amount. means that
The low-molecular-weight PTFE in which the difference P1-P2 is -0.07 or more can be produced, for example, by the above-described production method of the present disclosure. can be manufactured at low cost. If the difference P1-P2 is less than -0.07, the manufacturing cost may increase.
The difference P1−P2 is preferably greater than 0.00, more preferably 0.01 or more, and even more preferably 0.02 or more. The difference P1-P2 may also be 0.10 or less, more preferably 0.05 or less.
By performing the step (1) described above, the difference P1-P2 can be set within the above range.

FIG. 1 shows an example of P1 and P2 in the ESR spectrum.

The low molecular weight PTFE in the powder of the present disclosure has a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s. The melt viscosity is preferably 1.5×10 ³ Pa·s or more, more preferably 7.0×10 ³ Pa·s or more, and 3.0×10 ⁵ Pa·s or less. It is preferably 1.0×10 ⁵ Pa·s or less, more preferably 9.0×10 ⁴ Pa·s or less.

Regarding the composition, melting point, and molecular chain ends (the number of carboxyl groups, unstable terminal groups and their stabilization or amidation) of the low-molecular-weight PTFE in the powder of the present disclosure, the low-molecular-weight PTFE obtained by the production method of the present disclosure is described. The same one as above can be adopted.

The powder of the present disclosure may consist essentially of the low molecular weight PTFE. The amount of the low-molecular-weight PTFE with respect to the powder may be 95.0% by mass or more, preferably 99.0% by mass or more, and more preferably 99.5% by mass or more.

The powder of the present disclosure has a content of perfluorooctanoic acid and salts thereof of 1500 mass ppb or less. The amount of perfluorooctanoic acid and its salt in the powder may be 500 mass ppb or less, 300 mass ppb or less, 100 mass ppb or less, or 50 mass ppb or less. may be less than 25 mass ppb, may be 20 mass ppb or less, may be 15 mass ppb or less, may be 10 mass ppb or less, or may be less than 5 mass ppb may The lower limit is not particularly limited, and may be an amount below the detection limit.

In the powder of the present disclosure, the content (total amount) of perfluorocarboxylic acids having 4 to 16 carbon atoms and salts thereof may be 10000 mass ppb or less, may be 3000 mass ppb or less, and may be 2000 mass ppb or less. may be 1000 mass ppb or less, may be 500 mass ppb or less, may be 100 mass ppb or less, may be 50 mass ppb or less, or may be less than 25 mass ppb 20 mass ppb or less, 15 mass ppb or less, 10 mass ppb or less, or less than 5 mass ppb. The lower limit is not particularly limited, and may be an amount below the detection limit.

In the powder of the present disclosure, the amount of perfluorosulfonic acid having 4 to 16 carbon atoms and salts thereof may be less than 25 mass ppb, may be 20 mass ppb or less, or may be 15 mass ppb or less. , 10 mass ppb or less, or less than 5 mass ppb. The lower limit is not particularly limited, and may be an amount below the detection limit.

The powder of the present disclosure preferably has a specific surface area of 0.5-20 m ² /g.

The powder of the present disclosure preferably has an average particle size of 0.5 to 200 μm, more preferably 100 μm or less, even more preferably 50 μm or less, even more preferably 25 μm or less, and particularly preferably 10 μm or less. Since the powder has a relatively small average particle size, it is possible to form a coating film having superior surface smoothness, for example, when it is used as an additive for paint.

The powder of the present disclosure can be obtained, for example, by producing low-molecular-weight PTFE in powder form by the production method of the present disclosure described above. The powder of the present disclosure has excellent physical properties that are not inferior to conventionally known low-molecular-weight PTFE powders, and can be used in the same manner as conventionally-known low-molecular-weight PTFE powders, and can be used for the same purposes. can.

The low-molecular-weight PTFE obtained by the manufacturing method of the present disclosure and the powder of the present disclosure are used in molding materials, inks, cosmetics, paints, greases, members for office automation equipment, additives for modifying toner, and organic photoreceptor materials for copiers. , as an additive to the plating solution. Examples of the molding material include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide. The low-molecular-weight PTFE and the powder are particularly suitable as thickeners for grease.

The above-mentioned low-molecular-weight PTFE and the above-mentioned powder are used as additives for molding materials, for example, improving the non-adhesiveness and sliding properties of copy rolls, surface sheets for furniture, dashboards for automobiles, covers for home appliances, and other engineering plastic moldings. Applications to improve the texture of products, applications to improve the lubricity and wear resistance of mechanical parts that generate mechanical friction such as light load bearings, gears, cams, push-phone buttons, projectors, camera parts, and sliding materials, and engineering. It can be suitably used as a plastic processing aid or the like.

The low-molecular-weight PTFE and the powder can be used as an additive for paints for the purpose of improving the lubricity of varnishes and paints. The low-molecular-weight PTFE and the powder can be used as an additive for cosmetics for the purpose of improving the smoothness of cosmetics such as foundation.

The low-molecular-weight PTFE and the powder are also suitable for use in improving the oil repellency or water repellency of wax or the like, and in use for improving the slipperiness of grease or toner.

The low-molecular-weight PTFE and the powder can also be used as electrode binders for secondary batteries and fuel cells, hardness modifiers for electrode binders, water-repellent agents for electrode surfaces, and the like.

Grease can also be prepared using the low molecular weight PTFE or the powder and lubricating oil. Since the grease contains the low-molecular-weight PTFE or the powder and the lubricating oil, the low-molecular-weight PTFE or the powder is uniformly and stably dispersed in the lubricating oil. Excellent properties such as low hygroscopicity.

The lubricating oil (base oil) may be mineral oil or synthetic oil. Examples of the lubricating oil (base oil) include paraffinic and naphthenic mineral oils, synthetic hydrocarbon oils, ester oils, fluorine oils, and synthetic oils such as silicone oils. From the viewpoint of heat resistance, fluorine oil is preferable, and examples of the fluorine oil include perfluoropolyether oil, low polymer of trifluoroethylene chloride, and the like. The low polymer of ethylene trifluorochloride may have a weight average molecular weight of 500-1200.

The grease may further contain a thickening agent. Examples of the thickening agent include metal soap, composite metal soap, bentonite, phthalocyanine, silica gel, urea compounds, urea-urethane compounds, urethane compounds, and imide compounds. Examples of the metallic soap include sodium soap, calcium soap, aluminum soap, lithium soap and the like. Examples of the urea compounds, urea-urethane compounds and urethane compounds include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, urea-urethane compounds, diurethane compounds and mixtures thereof.

The grease preferably contains 0.1 to 60% by mass of the low-molecular-weight PTFE or the powder, more preferably 0.5% by mass or more, even more preferably 5% by mass or more, and 50% by mass or less. It is more preferable to include If the amount of the low-molecular-weight PTFE or the powder is too large, the grease may become too hard and may not exhibit sufficient lubricating properties. It may not be possible.

The grease may also contain solid lubricants, extreme pressure agents, antioxidants, oiliness agents, rust inhibitors, viscosity index improvers, detergent dispersants and the like.

EXAMPLES Next, the present disclosure will be described in more detail with reference to Examples, but the present disclosure is not limited only to these Examples.

Each numerical value in the examples was measured by the following method.

Reduction rate of heat of fusion was measured using a differential scanning calorimeter (DSC, trade name: DSC7020, manufactured by Hitachi High-Tech Science Co., Ltd.). Specifically, about 10 mg of PTFE was precisely weighed, placed in a special aluminum pan, heated to 200°C in a nitrogen atmosphere, held for 5 minutes, and further heated to 390°C at a rate of 10°C/min. The temperature was raised (first temperature rise) to sufficiently melt the crystals, and the heat of fusion was measured. Next, the temperature was lowered from 390° C. to 200° C. at a rate of 10° C./min and then raised from 200° C. to 390° C. at a rate of 10° C./min (second temperature rise) to measure the heat of fusion. Using the measured values of the heat of fusion at the time of the first temperature rise and at the time of the second temperature rise, the reduction rate of the heat of fusion was determined by the following formula.
Reduction rate of heat of fusion (%) = (heat of fusion at first temperature rise - heat of fusion at second temperature rise) / (heat of fusion at first temperature rise) x 100

Melt viscosity (MV)
In accordance with ASTM D 1238, a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die were used, and a 2 g sample that had been preheated at 380°C for 5 minutes was kept at the above temperature under a load of 0.7 MPa. measurements were taken.

Electron spin resonance method (ESR) measurement device: JES-FR30EX manufactured by JEOL Ltd.
Measurement temperature: 23±3°C
Microwave frequency: 9.42GHz
Microwave output: 0.4mW
Central magnetic field: 347.548mT
Sweep width: ±25mT
Sweep time: 60s
Time constant: 0.03s
Magnetic field modulation width: 0.32mT
Number of scans: 1 Modulation frequency: 100 kHz
Marker: Mn2 ⁺

Content of perfluorooctanoic acid and its salts (PFOA) The content of perfluorooctanoic acid and its salts was measured using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC/TQD). 5 ml of acetonitrile was added to 1 g of the powder to be measured, and ultrasonic treatment was performed for 60 minutes to extract perfluorooctanoic acid. The obtained liquid phase was measured using the MRM (Multiple Reaction Monitoring) method. Acetonitrile (A) and an aqueous solution of ammonium acetate (20 mmol/L) (B) were fed as mobile phases with a concentration gradient (A/B=40/60-2 min-80/20-1 min). A separation column (ACQUITY UPLC BEH C18 1.7 μm) was used, the column temperature was 40° C., and the injection volume was 5 μL. ESI (Electrospray ionization) Negative was used for the ionization method, the cone voltage was set to 25 V, and precursor ion molecular weight/product ion molecular weight was measured to be 413/369. The content of perfluorooctanoic acid and its salt was calculated using an external standard method. The limit of detection in this measurement is 5 ppb.

Content of perfluorocarboxylic acid having 4 to 16 carbon atoms and its salt (PFC) Using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD), perfluorocarboxylic acid having 4 to 16 carbon atoms and The salt was measured. The liquid phase extracted in the measurement of perfluorooctanoic acid was used as the solution, and the measurement was performed using the MRM method. As for the measurement conditions, the concentration gradient was changed from the measurement conditions for perfluorooctanoic acid (A/B = 10/90-1.5 min-90/10-3.5 min), and the precursor ion molecular weight/product ion molecular weight was Butanoic acid (4 carbon atoms) is 213/169, perfluoropentanoic acid (5 carbon atoms) is 263/219, perfluorohexanoic acid (6 carbon atoms) is 313/269, perfluoroheptanoic acid (7 carbon atoms) is 363/319, perfluorooctanoic acid (8 carbon atoms) is 413/369, perfluorononanoic acid (9 carbon atoms) is 463/419, perfluorodecanoic acid (10 carbon atoms) is 513/469, perfluoroundecanoic acid (11 carbon atoms) is 563/519, perfluorododecanoic acid (12 carbon atoms) is 613/569, perfluorotridecanoic acid (13 carbon atoms) is 663/619, perfluorotetradecanoic acid (14 carbon atoms) is 713 /669, perfluoropentadecanic acid (15 carbon atoms) was 763/719, and perfluorohexadecanoic acid (16 carbon atoms) was 813/769.
The total amount of perfluorocarboxylic acids having 4 to 16 carbon atoms and salts thereof was calculated using the following formula from the perfluorooctanoic acid content (X) obtained from the above measurement. The limit of detection in this measurement is 5 ppb.
(A _C4 + A _C5 + A _C6 + A _C7 + A _C8 + A _C9 + A _C10 + A _C11 + A _C12 + A _C13 + A _C14 + A _C15 + A _C16 )/A _C8 x X
A _C4 : Perfluorobutanoic acid peak area A _C5 : Perfluoropentanoic acid peak area A _C6 : Perfluorohexanoic acid peak area A _C7 : Perfluoroheptanoic acid peak area A _C8 : Perfluorooctanoic acid peak area A _C9 : Perfluorononanoic acid peak area A _C10 : Perfluorodecanoic acid peak area A _C11 : Perfluoroundecanoic acid peak area A _C12 : Perfluorododecanoic acid peak area A _C13 : Perfluorotridecanoic acid peak Area A _C14 : Peak area of perfluorotetradecanoic acid A _C15 : Peak area of perfluoropentadecanoic acid A _C16 : Peak area of perfluorohexadecanoic acid X: Perfluorohexadecanoic acid peak area calculated using the external standard method from the measurement results using the MRM method Fluorooctanoic acid content

Reduction rate of perfluorocarboxylic acids with 4 to 16 carbon atoms and their salts (PFC reduction rate)
The PFC content in the PTFE before irradiation and in the obtained low-molecular-weight PTFE was measured by the above method, and the measured values were used to obtain the PFC content according to the following formula.
PFC reduction rate (% by mass) = (PFC content in PTFE before irradiation - PFC content in obtained low-molecular-weight PTFE)/(PFC content in PTFE before irradiation) x 100

Oxygen concentration in the closed container was measured by analyzing the gas layer in the closed container by gas chromatography. Furthermore, it was confirmed that the oxygen concentration was 0.1% by volume or less (absence of oxygen) by changing the color tone of the oxygen detection paper enclosed in the sealed container from blue to pink.

Example 1
50 g of PTFE micropowder (PTFE-MP) (1) (heat of fusion reduction rate: 10.7%, PFOA amount: 155 mass ppb, PFC amount: 1008 mass ppb) was weighed into a barrier nylon bag.
Further, an iron-based self-reacting oxygen adsorbent (Ageless ZP-100 manufactured by Mitsubishi Gas Chemical Co., Ltd.) was enclosed as an oxygen adsorbent, and a barrier nylon bag was sealed by heat sealing. After confirming the absence of oxygen by the oxygen detection paper installed in advance in the bag, the PTFE micropowder in the bag was irradiated with 10 kGy of cobalt-60 γ rays at an ambient temperature of 20 to 45 ° C. to obtain a low molecular weight. A PTFE powder was obtained. The atmospheric temperature at the time of irradiation is the temperature including heat generated by irradiation (the same applies to the following examples and comparative examples).
Various physical properties of the obtained low-molecular-weight PTFE powder were measured. The above physical properties were measured after the bag was opened immediately after the irradiation and the powder was held in the air for about 30 minutes. Table 1 shows the results.

Example 2
A low-molecular-weight PTFE powder was obtained in the same manner as in Example 1, except that 100 kGy of cobalt-60 gamma rays was applied.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured in the same manner as in Example 1. Table 1 shows the results.

Example 3
A low-molecular-weight PTFE powder was obtained in the same manner as in Example 1, except that 400 kGy of cobalt-60 gamma rays was applied.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured in the same manner as in Example 1. Table 1 shows the results.

Examples 4-9
In the same manner as in Example 2, except that PTFE micropowder (2) to (7) having the heat of fusion reduction rate, PFOA amount, and PFC amount shown in Table 1 were used instead of PTFE micropowder (1). , to obtain a low molecular weight PTFE powder. Various physical properties of the obtained low-molecular-weight PTFE powder were measured in the same manner as in Example 1. Table 1 shows the results.

Comparative example 1
50 g of PTFE micropowder (1) was weighed into a bag made of barrier nylon. It was then sealed using a heat seal. The PTFE micropowder in the bag was irradiated with 100 kGy of cobalt-60 γ rays at an ambient temperature of 20 to 45°C to obtain a low molecular weight PTFE powder.
Various physical properties of the obtained low-molecular-weight PTFE powder were measured in the same manner as in Example 1. Table 1 shows the results.

Comparative example 2
Various physical properties were measured in the same manner as in Example 1 without irradiating the PTFE micropowder (1) with radiation. Table 1 shows the results.

Comparative example 3
50 g of PTFE micropowder (1) was weighed into an aluminum cup, and heat-treated at 100° C. for 3 hours using a hot air circulating electric furnace (high temperature constant temperature device STPH-202M manufactured by Espec Co., Ltd.). Various physical properties of the obtained low-molecular-weight PTFE powder were measured in the same manner as in Example 1. Table 2 shows the results.

Comparative example 4
A low-molecular-weight PTFE powder was obtained in the same manner as in Comparative Example 3, except that the heat treatment conditions were 100° C. for 0.5 hours. Various physical properties of the obtained low-molecular-weight PTFE powder were measured in the same manner as in Example 1. Table 2 shows the results.

Since the methods of Comparative Examples 3 and 4 require heating facilities, the production costs are high. On the other hand, the methods of Examples 1 to 9 do not require introduction of heating equipment. Moreover, a process such as moving the obtained low-molecular-weight PTFE from the irradiation equipment to the heating equipment is not necessary. Therefore, the methods of Examples 1 to 9 can improve productivity and suppress manufacturing costs.

Claims (2)

A powder comprising low molecular weight polytetrafluoroethylene,
The content of perfluorooctanoic acid and its salt is 1500 mass ppb or less,
The low-molecular-weight polytetrafluoroethylene has a melt viscosity at 380° C. of 1.0×10 ² to 7.0×10 ⁵ Pa·s, and in a first derivative spectrum obtained by measurement by an electron spin resonance method, , a powder in which the difference (P1-P2) between the signal intensity P1 at a g value of 2.020 and the signal intensity P2 at a g value of 2.023 is -0.07 or more. The powder according to claim 1, which has a specific surface area of 0.5 to 20 m ² /g.

Images